Centrifugal pump for pumping blood and other shear-sensitive liquids

ABSTRACT

The invention relates to a centrifugal pump comprising a pump head (1) and a drive (2) for delivering blood and other ?-sensitive fluids, such as cell-containing cleaning suspensions, for example, in blood-cleaning units, wherein the drive (2) has a drive rotor (64) with a rotor disk (8) which is provided with permanent magnets (7) which are assigned permanent magnets (33), fitted on the pump rotor (3), for the purpose of magnetic coupling, and are assigned in the drive to the magnetic coils (4) of a stator for the purpose of generating the rotary movement, and wherein the pump rotor axis (61) extends into the pump intake (11) and is magnetically centered in the pump intake (11).

The present invention relates to a centrifugal pump comprising a pumphead and a drive for delivering blood and other shear-sensitive fluids,such as cell-containing cleaning suspensions, for example, inblood-cleaning units.

Increasing use is being made of centrifugal pumps for deliveringsensitive fluids which can change in their composition owing toexcessive friction and shear stress. Particularly in medical andbiological applications, such pumps are used, For example, forheart-lung machines, for supporting the failing heart, as well as forpurpose of blood preparation for suspensions of cells or biologicallyactive particles. In this case, the rotor of the pump is mostly drivenvia a conventional motor, it being the case either that the energy isinjected into the magnets of the pump rotor via an additional magnetdisk of the drive, or that the magnets of the pump rotor are lengthenedin the axial direction and are therefore arranged as rotor of electricmotor in the rotary field of the stator. Combinations of disk-rotormotors with magnetic couplings have also been described (for exampleEP-401 761-A2, Ebara Corp.), but they also provide for structuralseparation of the magnetic circuits of the rotor and the pump. Thesearrangements entail a substantial overall height of the pump, and thisis disadvantageous.

Particularly in the case of blood pumps for cardiac support, which canbe implanted or are fitted near the body, but also in the case ofbedside mounted units for blood purification and in other applications,the aim is a pump/drive combination of low overall height and of lowvolume and weight. A pump of low design is proposed in the PCTapplication WO-92/03 181-A1, Baylor College. In this pump, the magneticdisk driven by the disk-rotor stator is used simultaneously for themagnetic coupling of the rotor. In the case of a motor of this design, aconsiderable volume of iron is required for the magnetic return pathand, at the same time, a relatively low magnetic saturation is achieved.

A pump has become known (via Schima et al., Artificial Organrs 19:7(1995), Pages 639-643) in which coupling of the magnetic circuits of themotor and pump rotor is performed. However, with this arrangement therotor is stabilized by three supporting points on the pump base, andthis can lead to increased blood traumatization during the conveyance ofblood. Furthermore, a pump has become known (Yamane et al: ArtificialOrgans 19:7 (1995), Pages 625-630) in which there is a magneticsuspension of the rotor on the tip facing the intake, fit being the casethere, however, that because of the unfavorable distribution of themagnetic forces the overall height must be relatively large and theintake is disturbed. Finally, mention may be made of a centrifugal pump(Akamatsu et al: Artificial Organs 19:7 (1995), Pages 631-634), in whichin addition to the magnetic injection of the rotational energy viaadditional magnet disks, electromagnetic stabilization of the rotor isprovided by complete floating in the housing. However, thisstabilization requires a relatively large coil apparatus on thecircumference of the pump.

It is the object of the present invention to create and improve the pumpof the type described at the beginning and the drive therefore, in whichthe existing disadvantages are avoided. In particular, the pump isintended to have a low overall height and low volume and weight, as wellas a high operational reliability. The unfavorable mechanical effects onthe delivered medium, such as high shear forces, are to be avoided.

The present invention is defined by virtue of the fact that the drivehas a drive rotor with a rotor disk which is provided with permanentmagnets which are assigned permanent magnets, fitted on the pump rotor,for the purpose of magnetic coupling, and are assigned in the drive tothe magnetic coils of a stator for the purpose of generating the rotarymovement, and in that the pump rotor axis extends into the pump intakeand is magnetically centered in the pump intake.

According to a further characteristic of the invention, for the purposeof magnetically centering the pump rotor axis the latter has a permanentmagnet, and the pump intake has one or more annularly arranged magnetspolarized in the same direction. The magnets can be permanent magnets orelectromagnets. The magnets can preferably be arranged in the wall ofthe pump intake, an annular flow channel being formed between the pumprotor axis and the wall of the pump intake. The permanent magnet on thepump rotor axis or the pump rotor can be offset in the axial directionwith respect to the annularly arranged magnets of the pump intake, inorder to increase the centering effect. Controls are arranged on thewall of the pump intake or on the pump rotor axis, magnets or their yokeprojecting if appropriate into the region of the control surfaces. Oneor both magnets of the pump intake can have oblique or contouredsurfaces on their sides facing one another.

In accordance with the preferred feature of the invention, the bearingof the pump rotor is constructed as a magnetic bearing on the rear wallof the pump head, this bearing comprising one or more permanent magnetsIn the rear rotor tip on the rear side of the rotor and permanentmagnets and/or electromagnets in the bearing shell formed by the rearwall. The bearing of the pump rotor on the rear wall of the pump headcan be constructed as a magnetic bearing, on the rear wall of the pumphead, this bearing comprising one or more permanent magnets in the rearrotor tip on the rear side of the rotor and permanent magnets and/orelectromagnets in the bearing shell formed by the rear wall.Alternatively, the bearing seat of the pump rear wall can be designedwith a flat central surface for the rear rotor tip, which surfacepermits lateral excursions of the rear rotor tip in a limited range oftypically 0.5 to 3 mm diameter.

According to further features, the pump rotor has on its rear side vaneswhich during rotation produce a dynamic pressure by virtue of adifferent inclination of the vane surfaces on the upstream side anddownstream side, and thereby facilitate and/or cause lifting of the pumprotor from the rear wall. The pump rotor can be designed with exposedrotor vanes in which there are recessed magnets whose magnetization runstransverse to the rotation axis of the pump rotor axis. There can beprovided on the underside of the rotor vanes support surfaces whichcause an axial force during rotation in fluid. There can be provided onthe topside of the rotor vanes support surfaces which cause an axialforce during rotation in fluid.

The rotor vanes can have different surfaces and/or angles of attack, andthereby cause an asymmetrical flow on the rear wall of the pump.

The drive itself can be advantageously constructed in several ways.According to one variant, the drive rotor comprises an upper and a lowerrotor disk and the magnet coils of the stator are situated between thetwo rotor disks. For the purpose of reducing the stray magnetic fieldthe lower rotor disk of the drive can have a magnetic return path in theform of a magnetically conductive disk or ring made, for example, fromsoft iron. For the purpose of improving the efficiency of the drive thecoils can be arranged in a plurality of offset layers and/or woundinclined to the plane of the coil form. Alternatively, the drive rotorcan comprise an upper rotor disk, and provided in the stator instead ofthe lower rotor disk is a magnetic yoke which interconnects the ironcores of the magnet coils of the stator. To prevent or reduce eddycurrents, circular and/or radial depressions or also slots can beprovided in the rear wall of the pump or, in the case of a separablepump and drive, on the covering wall of the drive.

According to a further feature, it is provided that in each case a pumphead is fitted on both sides of the drive in the axial direction,preferably for the purpose of simultaneously supporting/substitutingleft-hand and right-hand halves of the heart, it being possible for thesize and rotor configuration of the two pump heads to differ in order toachieve a pumping capacity matched to the physiological requirements.The pump head and the drive are preferably separated from one another inorder to replace the pump head or the drive alone.

The advantageous features and improvements relate both to the pumpitself and to its drive and are constitute an advantageous inventionboth separately from one another and in combination.

The invention will be explained below in more detail with the aid of thedrawings.

FIG. 1 shows a first embodiment of the pump according to the invention,and

FIGS. 2a, 2b, 2c and 3 are sections along the line A--A through thepump, with a different design of the rotor and the stator windings, thehousing parts having been left out to improve clarity. FIG. 2c shows, byway of example, the rear view of a rotor without a closed rear wall,with exposed vanes and magnets integrated therein.

FIG. 4 shows an embodiment with electromagnets, a detailed view relatingto the bearing of the rotor tip in the rear wall of the pump being givenin FIG. 5.

FIG. 6 shows a design with a motor and two pump heads.

FIG. 7 represents a detail of a side view of the side of a rotor withrear wall, and

FIG. 8 represents the rear view of this rear wall.

FIG. 9 shows an embodiment of electromagnets on the rotor tip for FIG.4.

FIG. 10 shows an embodiment of the rear rotor tip in a bearing withoutcentering function.

FIG. 11 to FIG. 14 show embodiments for the magnetic bearing of therotor tip with arrangements of control surfaces either in the pumphousing or in the inflow region of the rotor, and a possiblemultiplication of the magnets in the inflow region.

FIGS. 15 and 16 show the plan view of the rear side of the rear wall ofthe pump head and an or associated cross-section with arrangeddepressions for minimizing the eddy current losses.

FIG. 17 shows the design of a rotor vane with supporting surface nearthe base. Finally,

FIG. 18 is a diagram of a rotor with differently shaped vanes forachieving a flow eddy with a center point off the rotor axis.

As FIG. 1 shows in cross-section, the pump head 1 contains a pump rotor3 with rotor blades 32, which causes the fluid entering the pump headthrough the pump intake 11 to rotate and presses it through the pumpoutlet 12 by means of the centrifugal force produced by the rotation.

The rotary movement of the pump rotor 3 is injected via a magneticfield. Both the pump rotor 3 and the two rotor disks 5, 8 of the driverotor 64 of the drive 2 have permanent magnets (drive magnets 7, 33),the drive magnets 7 of the motor rotor disks 5, 8 being in each casealternately differently polarized. In this case, use is preferably madeof 6, 12, 18 or 24 magnets per disk. Rotor disks 5, 8 of the drive 2 arearranged rotatably, either the axis 9 being rotatable, or the two rotordisks 5, 8 being mounted on a fixed axis 9 via one or more bearings 10.Arranged between the two rotor disks 5, 8 is a stator or coil form 13with magnet coils 4 which are connected via the supply lead 41 to theelectric rotary field, and thereby generate the electromagnetic motorrotary field. The required commutation of the electric field ispreferably performed by means of an electronic circuit in a known way byevaluating the backward EMF, it being possible for this circuit also tobe integrated into the drive itself.

The magnets 33 in the pump rotor can be arranged either parallel to thedrive magnets 7 of the drive 2, or, preferably as represented in FIG.2a, be arranged transverse to the drive magnets 7 for the purpose ofreducing the forces acting laterally on the pump rotor 3. The magneticfield lines 44, and thus the forces, then act to a considerable extenttransverse to the bearing axis, the tilting torque being substantiallyreduced as a result.

The coils 14, 15, 16, shown in FIGS. 2a and 2b and 3, of the coil form13 can either be situated next to one another or, as shown in FIG. 2a,be arranged in a plurality of layers offset one above another or, asshown in FIG. 3, be arranged in an obliquely overlapping fashion. Ironcores or beds of iron cores 45 can be provided in order to increase themagnetic flux.

As represented in FIG. 1, in order to ensure as high as possible a fieldstrength of the field generated by the permanent magnets 7, and thus toensure good efficiency for the motor, it is possible to arrange belowthe permanent magnets of the lower rotor disk 5 a disk or ring 6 madefrom soft iron, which minimize the stray fields on the rear side of thedrive 2 and over the pump rotor 3. If the magnets 33 of the pump rotorare arranged in the same direction as the drive magnets 7, it is alsopossible for a soft iron disk or soft iron ring to be arranged over themfor the magnetic return path. As represented in FIGS. 2b and 2c, thepump rotor 3 can, however, also be designed with exposed vanes 51 intowhich magnets 50 for magnetizing transverse to the axis are recessed.

The pump rotor 3 is mounted magnetically in the intake. Accommodated forthis purpose on its pump rotor axis 61 or rotor tip 49 thereof is apermanent magnet 34 opposite which there is situated around the intake11 an annular magnet arrangement 35 polarized essentially in the samedirection. As represented in FIG. 1, this magnet 35 is preferablydesigned as a purely permanent magnet. As shown in FIG. 4 and FIG. 9,however, it is also possible to provide additional, electromagneticcoils 42 with iron yokes 43, for the purpose of improving thestabilization. The magnets 35 are preferably arranged in the wall 62 ofthe pump intake 11, in order not to impede the intake through theannular flow channel 63.

The bearing on the rear wall 20 of the pump head can be designed as apivot bearing (FIG. 1). In order to lower the friction and thus the heatand destruction of blood produced at the bearing tip 36 in the bearingshell 37, it is possible, moreover, to provide a partial or completemagnetic bearing 48. FIG. 5 shows a possible design of this magneticbearing, which has a permanent magnet 39 in the rear rotor tip and haselectromagnetic coils 46 in the bearing shell and, additionally, canhave a permanent magnet 47. The check-back signal For the magnetposition can be determined in this case either from the impedance of thecoils 46 or by position sensors.

As FIG. 10 shows, the lower rotor bearing can also be designed with aflat bearing seat 52 in which the bearing tip 36 of the rotor rear sidecan execute transverse movements within a certain range withoutmechanical limitation, in order to permit the bearing seat to be cleanedautomatically of blood constituents, there being a need to provide aflat region of typically 0.5 to 3 mm diameter. The bearing seat 52 canpreferably be made in this case from ceramic or high-density plastic.

As shown in FIG. 7 in the side view of the rotor rear side, and in FIG.8 in a plan view thereof, it is possible to fit on the rear side of thepump rotor 3 7,vanes 27 whose shape facilitates controlled lifting ofthe rotor from the pump rear wall 20 and the middle piece thereof.Because of the rotation 28 of the pump rotor 3, the incoming fluid 29,which strikes the vanes 27 produces a dynamic pressure on the flatinclined upstream side, while low corresponding counter-pressure isbuilt up on the steeply set rear side 31 of the vanes. This makes iteasy for the rotor to run up on a liquid layer of controlled thickness(depending on the speed, the counter-pressure, the viscosity of theliquid and the spacing of the vanes 27 from the rear wall 20 of the pumphead 1), and minimizes the force to be absorbed by the magnet bearings.Moreover, this equalization of the different pressures on the rotorunderside and topside can be performed by recesses 18 in the pump rotoror by shaping the rotor in self-supporting vanes.

Furthermore, either an asymmetrical configuration of the permanentmagnet 47 (FIG. 5) or a bipartite outlet can be provided for equalizingthe forces on the circumference of the rotor, which act eccentrically inthe case of a single outlet.

In order to render possible multiple use of the drive in the case ofpump heads which are to be used only once, or in the case of replacementof the pump head, the pump head and drive can be designed separatelyfrom one another, as represented in FIG. 1. For use with cell-containingfluids such as, for example, blood and other fluids sensitive tointernal friction (=shear stress), the pump head is to be designed suchthat zones of higher shear forces are avoided as far as possible.

Finally, as represented in FIG. 6, the pump can be fitted with two pumpheads 1 in order to permit both the left-hand and the right-handventricle to be supported by one system. The pump heads and rotors canbe designed with a different diameter and/or with a different rotorconfiguration in order to adapt to the different required pumpingcapacities of the two ventricles.

As represented in FIGS. 11 to 14, control surfaces 54, 58 can bearranged in the inflow region of the pump an order to enlarge thehydrodynamically active gap between the rotor and housing, and toincrease the efficiency. As shown in a lateral view in FIG. 11 and inplan view in FIG. 12, these control surfaces are preferably fitted onthe inside of the wall 62 of the pump intake 11, it being possible topull the magnet 35 forward into the control surfaces in order to shortenthe magnetically active air gap or to provide iron yokes 55 for relayingthe magnetic field into the vane. These control surfaces 54 can also beset obliquely or be curved in this case in order to improve thehydrodynamic properties.

It is shown, moreover, in FIG. 11 that the drive can also be carried outonly with a single top rotor disk 8, the magnetic feedback taking placein this case on the rear side of the motor via an annular magnet yoke 53which interconnects the iron core 45 of the motor coils 14, 16 (see alsoFIGS. 2a to 3).

Furthermore, as shown in FIG. 11, instead of a straight axially parallelwall the magnets 34, 35 can have an obliquely set or contoured wall inorder to achieve a controlled variation of the air gap width, and thusof the magnetically generated restoring force in the case when the rotoris lifted. Given a contoured wall, the magnet 34 can, for example, bedomed (indicated by dashes in FIG. 11).

Instead of stationary control surfaces 54 on the pump housing, it isalso possible to provide an arrangement of control surfaces 58 on thepump rotor 3 itself, as is represented in FIGS. 13 and 14, it also beingpossible in this case to provide an extension of the magnet 34 intothese control surfaces 58 or iron yokes 55, in order to reduce themagnetically active air gap.

In the case of a metallic rear wall 20 of the pump, which does, afterall, simultaneously represent the covering wall of the drive, the movingmagnetic field produces eddy currents between the drive rotor disk 8 andpermanent magnet 33 of the pump rotor. It is possible for the purpose ofreducing these eddy currents to increase the electrical resistance ofthe rear wall 20 by means of depressions 59. 60, which are representedin FIGS. 15 and 16. These depressions can be provided in a circulararrangement 59 and/or in a radial arrangement 60, it being necessary totake account of the mechanical strength of the pump and of the drive inthe case of the number and shaping. If the rear wall of the pump 20 andthe covering wall of the drive are of separate design in order to permitthe pump and drive to be more easily separated, depressions in thecovering wall of the drive can also be designed as slots.

As is shown in FIG. 17, the pump rotor vanes can also be equipped with asupporting surface 57 in the vicinity of the pump base 20, in order topermit a reduction, caused hydrodynamically by the rotation, in thecontact pressure in the bearing, or a lifting of the rotor. It is alsopossible to arrange supporting surfaces 67 on the other side of the pumprotor.

Finally, it is shown in fig. 18 that in order to achieve an asymmetricalflow near the base, and thus an increase in the washout in the vicinityof the axis, the vanes of the rotor can be of different (asymmetrical)design, it being possible to provide a different height of the vane, butalso a different inclination of the vanes (see the different shape ofthe surfaces 68).

What is claimed is:
 1. A centrifugal pump comprising a pump head (1) anda drive (2) for delivering blood and other shear-sensitive fluids, suchas cell-containing cleaning suspensions, for example, in blood-cleaningunits, wherein the drive (2) has a drive rotor (64) with a rotor disk(8) which is provided with permanent magnets (7) which are assignedpermanent magnets (33), fitted on the pump rotor (3), for the purpose ofmagnetic coupling, and are assigned in the drive to the magnetic coils(4) of a stator for the purpose of generating the rotary movement, andwherein the pump rotor axis (61) extends into the pump intake (11) andis magnetically centered in the pump intake (11).
 2. The pump as claimedin claim 1, wherein for the purpose of magnetically centering the pumprotor axis (61) the latter has a permanent magnet (34), and the pumpintake (11) has one or more annularly arranged magnets (35) polarized inthe same direction.
 3. The pump as claimed in claim 2, wherein themagnets (35) are permanent magnets.
 4. The pump as claimed in claim 2,wherein the magnets (35) are electromagnets.
 5. The pump as claimed inclaim 1, wherein the magnets (35) are arranged in the wall (62) of thepump intake (11), and an annular flow channel (63) is formed between thepump rotor axis (61) and the wall of the pump intake (11).
 6. The pumpas claimed in claim 1, wherein the permanent magnet (34) on the pumprotor axis (61) or the pump rotor (3) is offset in the axial directionwith respect to the annularly arranged magnets (35) of the pump intake(11), in order to increase the centering effect.
 7. The pump as claimedin claim 1, wherein controls (54, 58) are arranged on the wall (62) ofthe pump intake (11) or on the pump rotor axis (61), magnets (34 or 35)or their yoke projecting if appropriate into the region of the controlsurfaces (54, 58).
 8. The pump as claimed in claim 1, wherein one orboth magnets (34 or 35) of the pump intake have oblique or contouredsurfaces (65) on their sides facing one another.
 9. The pump as claimedin claim 1, wherein the direction of magnetization of the magnets (33)on the pump rotor (3) is aligned transverse to the direction ofmagnetization of the drive magnets (7) (FIGS. 2a to 3).
 10. The pump asclaimed in claim 1, wherein the bearing (66) of the pump rotor (3) isconstructed as a magnetic bearing on the rear wall (20) of the pump head(1), this bearing comprising one or more permanent magnets (39) in therear rotor tip (36) on the rear side of the rotor (3) and permanentmagnets (47) and/or electromagnets (46) in the bearing shell formed bythe rear wall (20) (FIG. 5).
 11. The pump as claimed in claim 1, whereinthe bearing seat (52) of the pump rear wall (20) is designed with a flatcentral surface for the rear rotor tip (36), which surface permitslateral excursions of the rear rotor tip in a limited range of typically0.5 to 3 mm diameter, (FIG. 10).
 12. The pump as claimed in claim 1,wherein the pump rotor (3) has on its rear side vanes? (27) which duringrotation produce a dynamic pressure by virtue of a different inclinationof the vane surfaces on the upstream side (30) and downstream side (31),and thereby facilitate and/or cause lifting of the pump rotor (3) fromthe rear wall (20) (FIGS. 7, 8).
 13. The pump as claimed in claim 1,wherein the pump rotor (3) is designed with exposed rotor vanes (51) inwhich there are recessed magnets (50) whose magnetization runstransverse to the rotation axis of the pump rotor axis (61) (FIGS. 2b,c).
 14. The pump as claimed in claim 1, wherein there are provided onthe underside of the rotor vanes (51) support surfaces (57) which causean axial force during rotation in fluid (FIG. 17).
 15. The pump asclaimed in claim 1, wherein there are provided on the topside of therotor vanes (51) support surfaces (67) which cause an axial force duringrotation in fluid (FIG. 17).
 16. The pump as claimed in claim 1, whereinthe rotor vanes have different surfaces (68) and/or angles of attack,and thereby cause an asymmetrical flow on the rear wall of the pump(FIG. 18).
 17. The pump as claimed in claim 1, wherein the drive rotor(64) comprises an upper and a lower rotor disk (8, 5), and the magnetcoils (4) of the stator are situated between the two rotor disks (5, 8).18. The pump as claimed in claim 1, wherein for the purpose of reducingthe stray magnetic field the lower rotor disk (5) of the drive (2) has amagnetic return path in the form of a magnetically conductive disk orring (6) made, for example, from soft iron.
 19. The pump as claimed inclaim 1, wherein for the purpose of improving the efficiency of thedrive the coils (14, 15, 16) are arranged in a plurality of offsetlayers and/or wound inclined to the plane of the coil form (13) (FIGS.2, 3).
 20. The pump as claimed in claim 1, wherein the drive rotor (64)comprises an upper rotor disk, and provided in the stator instead of thelower rotor disk is a magnetic yoke (53) which interconnects the ironcores (45) of the magnet coils (4) of the stator (FIG. 11).
 21. The pumpas claimed in claim 1, wherein circular and/or radial depressions (59,60) or also slots are provided in the rear wall of the pump or, in thecase of a separable pump and drive, on the covering wall of the drive(FIGS. 15, 16).
 22. The pump as claimed in claim 1, wherein in each casea pump head (1) is fitted on both sides of the drive (2) in the axialdirection, preferably for the purpose of simultaneouslysupporting/substituting of the left and right heart, it being possiblefor the size and rotor configuration of the two pump heads to differ inorder to achieve a pumping capacity matched to the physiologicalrequirements.
 23. The pump as claimed in claim 1, wherein the pump head(1) and the drive (2) can be separated from one another in order toreplace the pump head (1) or the drive (2) alone.